The invention relates to a process for recycling electrode materials from discharged, spent lithium batteries in which negative-electrode materials from the lithium/transition-metal mixed oxide class of compounds from discharged, spent lithium batteries can, after comminution of the electrode constituents, be re-synthesized into chemically identical products as employed for the production of the batteries, by mechanical and extractive processing of these constituents with the aim of removing positive electrode constituents and other secondary constituents, such as binders and other processing auxiliaries, followed by controlled high-temperature treatment, without leaving thermal decomposition products behind.
The demand for rechargeable lithium batteries is high and will increase much more considerably still in the future. The reasons for this are the high energy density that can be achieved, and the low weight of these batteries. These batteries are used in mobile telephones, portable video cameras, laptops, etc.
As is known, the use of metallic lithium as positive electrode material results, owing to dendrite formation during dissolution and deposition of the lithium, in inadequate cycle stability of the battery and in a considerable safety risk (internal short-circuit) (J. Power Sources, 54 (1995) 151).
These problems have been solved by replacing the lithium-metal positive electrode by other compounds which can reversibly intercalate lithium ions. The principle of functioning of lithium ion batteries is based on the fact that both the negative-electrode and positive-electrode materials can reversibly intercalate lithium ions, i.e. the lithium ions migrate out of the negative electrode during charging, diffuse through the electrolyte and are intercalated in the positive electrode. During discharging, the same process occurs in the opposite direction. Owing to this mechanism of functioning, these batteries are also referred to as xe2x80x9crocking-chairxe2x80x9d, or lithium ion batteries.
The resultant voltage of a cell of this type is determined by the lithium intercalation potentials of the electrodes. In order to achieve the highest possible voltage, negative-electrode materials which intercalate lithium ions at very high potentials and positive-electrode materials which intercalate lithium ions at very low potentials (vs. Li/Li+) must be used. Negative-electrode materials which satisfy these requirements are LiCoO2 and LiNiO2, which have a layered structure, and LiMn2O4, which has a cubic three-dimensional network structure. These compounds eintercalate lithium ions at potentials of around 4 V (vs. Li/Li+). In the case of the positive-electrode compounds, certain carbon compounds, such as, for example, graphite, meet the requirement of low potential and high capacity.
The electrolytes used are mixtures which contain aprotic solvents in addition to a conductive salt. The most frequently used solvents are ethylene carbonate (EC),propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC) andethyl methyl carbonate (EMC). Although a whole series of conductive salts is being discussed, LiPF6 is used virtually without exception.
Negative-electrode, materials in accumulators are functionally constructed multicomponent mixtures. The actual active material, which, in commercially available lithium accumulators, consists of binary lithium/transition metal mixed oxides, is mixed with auxiliaries which influence both the electrochemical characteristics of the electrodes and the processing properties.
Use is made of graphite and technical-grade carbon as electrically conductive auxiliaries, polymers (such as, for example, polyvinylidene fluoride and butadiene-styrene copolymers, and chemically modified celluloses) as binders, which improve the adhesion to a metallic support, and mixture modifiers for improving the processing properties of the composite mixture.
In addition, the electrochemically active electrode pack, besides metallic support material (copper and aluminum foil for positive-electrode and negative-electrode material), also comprises a separator-foil (polyalkene, preferably polypropylene) and as electrolyte, a solvent mixture in which the conductive salts is dissolved.
The separation. and processing of the various constituents is very complex. In general, processing methods involving a plurality of technologically different process steps are used for this purpose, but they generally only enable the recovery of the individual transition metals in the form of simple salts.
There is a need for an economical process which enables valuable negative-electrode raw material to be recovered from spent lithium batteries without following the circuitous route via re-synthesis from dissolved salts obtained by digestion methods or other degradative processes.
For the recovery of metals from secondary raw materials of a general nature intended for recycling, use is generally made of digestion methods, in which the metals are recycled in dissolved or adsorbed form, where the recycling does not consist in the original use of the materials, but in which the recovered metals are employed for neosynthetic processes.
Thus, U.S. Pat. No. 5,443,619 describes a process in which the metals of interest are recovered by extraction from aqueous solutions. The recovery processes used include leaching processes, as described, for example, in U.S. Pat. No. 5,364,444. The recovery of valuable metals from spent catalysts by a combination of various chemical processing steps and selective extraction is described in EP 652978.
The recovery of metallic raw materials from batteries is a technologically relatively new area. Processing methods have been described for various types of battery: for example, the recovery of manganese using a combination of wet digestion methods and a roasting process has been described (Progress in Batteries and Battery Materials, 13 (1994), 367 ff). In U.S. Pat. No. 5,407,463, the recovery of the metallic raw materials cadmium, nickel and iron from Ni/Cd batteries is achieved by wet acidic digestion, extraction and wet-chemical separation.
In the treatment of lithium batteries in general and of lithium accumulators in particular, similar working methods are used for material recovery, in particular of the metals present, with adaptation of the process steps to the specific material properties of these batteries. Thus, JP 11-6020 and Hydrometallurgy 47 (1998) pg. 259, describe the extractive recovery of cobalt from lithium cobaltate-containing batteries using a combination of electrochemical and wet-chemical methods. A further process for the recovery of raw materials from lithium batteries is published in the symposium proceedings xe2x80x9cTreatment and Minimization of Heavy Metal containing Wastesxe2x80x9d, Proc. Int. Symp. (1995) pg. 257. In this process, lithium and manganese are converted into carbonates. The metals iron, nickel and chromium are recovered separately as dissolved nitrates by acidic digestion.
The object of the invention is therefore to provide the recycling of negative-electrode materials, consisting of lithium/transition metal mixed oxides, from spent, discharged lithium batteries, which materials can be re-used in the production of lithium batteries.
The object according to the invention is achieved by a process for the recovery of negative-electrode materials from the lithium/transition metal mixed oxide class of compounds from spent lithium batteries, comprising the following steps:
i) uncovering of the electrode pack consisting at least of the positive-electrode unit, the separator parts, the electrolyte and the negative-electrode unit,
ii) extraction of the electrode pack with an organic solvent,
iii) drying of the extracted electrode pack,
iv) mechanical separation of the positive-electrode unit from the electrode pack treated in this way,
v) grinding and classification of the residual electrode pack obtained from step iv,
vi) subjection of the material obtained from step v to high-temperature treatment at temperatures of from about 300 to about 700xc2x0 C. under such conditions that essentially no thermal decomposition products remain in the negative electrode materials recovered here.
The present invention relates to undoped and doped, ternary or multinary mixed oxides as negative electrode materials. The present invention also relates to other lithium intercalation compounds which are suitable for 4 V negative electrodes.
It has been found that the process according to the invention enables the selective removal of the secondary constituents, additives and auxiliaries, such as foils, binders, and carbon, from the recyclable negative-electrode material.
It has also been found that 1,2-dimethoxyethane, dimethyl carbonate, ethyl acetate and acetone are particularly suitable solvents for the usual conductive salts.
Surprisingly, it has been found that regulated high high-temperature treatment of the negative-electrode material enables the material to be restructured.
A chemically and structurally identical negative electrode material as previously used in the battery can be recovered in a few simple and technologically well-controlled process steps while saving time and large amounts of energy.